Journal of Organic Chemistry p. 3925 - 3938 (2013)
Update date:2022-08-15
Topics:
Douglas, James
Taylor, James E.
Churchill, Gwydion
Slawin, Alexandra M. Z.
Smith, Andrew D.
A chiral NHC catalyzes the asymmetric formal [2 + 2] cycloaddition of alkylarylketenes with both electron-deficient benzaldehydes and 2- and 4-pyridinecarboxaldehydes to generate stereodefined β-lactones. In the benzaldehyde series, optimal product diastereo- and enantiocontrol is observed using 2-nitrobenzaldehyde (up to 93:7 dr (syn:anti) and 93% ee). Substituted 2- and 4-pyridinecarboxaldehydes are also tolerated in this process, generating the corresponding β-lactones in good yield and enantioselectivity, although the diastereocontrol in these processes is highly dependent upon the aldehyde substitution. These processes are readily scalable, allowing multigram quantities of the β-lactone products to be prepared. Derivatization of these products, either through ring opening into the corresponding stereodefined β-hydroxy and β-amino acid derivatives without loss of stereochemical integrity or via cross-coupling, is demonstrated.
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